P-N-P ligand

Abstract

A new P-N-P ligand is useful in ethylene oligomerizations. In combination with i) a source of chromium; and ii) an activator such as methylalumoxane; the ligand of this invention may be used to prepare an oligomer product that contains a mixture of high purity alpha olefins. In a preferred embodiment, the ligand of this invention enables a selective oligomerization in which the majority of the liquid product is a mixture of hexene and octene. The amount of by-product polymer that is produced in preferred oligomerization reactions is advantageously low.

The invention claimed is: 
     
       1. A process for the oligomerization of ethylene, wherein said process comprises contacting ethylene under oligomerization conditions with a catalyst system comprising
 i) a source of chromium; 
 ii) a ligand defined by the formula 
 
       
         
           
           
               
               
           
         
         
           wherein Ar 1  is selected from the group consisting of aromatic hydrocarbyl and aromatic heterohydrocarbyl; Ar F  is an aromatic fluorocarbyl oxide; Ar 3  and Ar 4  are independently selected from the group consisting of aromatic hydrocarbyl, aromatic heterohydrocarbyl and aromatic fluorocarbyl oxide; and R 1  is selected from the group consisting of hydrocarbyl and heterohydrocarbyl; and 
         
         iii) an activator. 
       
     
     
       2. The process of  claim 1  when undertaken at a temperature of from about 10° C. to about 300° C. and a pressure of from about 5 atmospheres to about 150 atmospheres. 
     
     
       3. The process of  claim 1  wherein said source of Cr is selected from the group consisting of chromium chlorides, chromium carbonyl, chromium carboxylates and chromium acetylacetonate. 
     
     
       4. The process of  claim 1  wherein said activator comprises methylaluminoxane. 
     
     
       5. The process of  claim 1  which is further characterized by producing a liquid product stream which contains greater than about 25 weight % octene-1.